The present invention relates to a process for the preparation of diacetoneketogulonic acid, which is a valuable intermediate product used in the preparation of vitamin C.
As a rule, the starting material used for the preparation of diacetoneketogulonic acid is diacetonesorbose. It can be oxidized to diacetoneketogulonic acid using inorganic oxidizing agents, such as HNO.sub.3, H.sub.2 O.sub.2, KMnO.sub.4 or in particular hypochlorite. These processes, however, are disadvantageous since in some cases very large amounts of inorganic salts are formed. These are a considerable load on the waste water.
Recently, therefore, particular interest has been aroused by electrochemical oxidation. This process is particularly advantageous because in addition to the anodic oxidation, hydrogen is generated at the cathode. The latter is required within the framework of the total synthesis of vitamin C. Electrochemical oxidation has, however, the disadvantage that a sufficiently high conversion requires very long electrolysis times and a very large electrode surface. The large electrode surfaces and the short lifetime of the electrodes, due to the long electrolysis times, lead to considerable costs. Moreover, with the very long electrolysis times there is a danger of further oxidation of the product. This affects the yield, which as a rule is lower for electrochemical oxidation than for wet-chemical oxidation.
Oxidation with air or other oxygen-containing gases, acting under catalysis by noble metals, in principle is extremely interesting. However, it is subject to the same disadvantages. Although this oxidizing agent is available in virtually unlimited amounts and therefore can be employed inexpensively, considerable disadvantages result from the long reaction times necessary and the further oxidation of the product which then occurs.